The present invention applies to the rolling of an aircraft on the ground, in particular an airplane, civil or military, for transporting passengers or merchandise (freight), or else a drone (pilotless aircraft). It relates more particularly to an automatic longitudinal guidance making it possible to slave the speed of an aircraft rolling on the ground to a speed profile (which is associated with a ground trajectory).
Within the framework of the present invention, the following meanings are implied:                rolling on the ground implies any type of possible rolling of an aircraft, such as rolling on a landing runway in the course of the landing and takeoff phases, or rolling on trafficways or on maneuvering areas, in particular; and        automatic longitudinal guidance implies the action of a system capable of ensuring, partially or totally, that is to say without aid or with the partial aid of a (human) operator, the driving of an aircraft on the ground according to its longitudinal axis.        
Currently, the (human) pilot controls the longitudinal movements of the aircraft (that is to say its speed and/or its acceleration) on the ground, with the aid of manual piloting facilities (for example the lever for controlling the thrust of the engines and the pedals of the brakes), along a ground trajectory. These facilities make it possible to control actuators of the aircraft capable of influencing the longitudinal movements of the aircraft, in particular by way of the engines and brakes or any type of means liable to act on the longitudinal movements of the aircraft.
The term ground trajectory designates the pathway followed by the aircraft on an airport domain such as an aerodrome or an airport, including in particular the takeoff and landing runways, the trafficways or taxiways, the turn-around areas, the waiting zones, the stop bars, the stopping positions (stand), the maneuvering areas, and the parking areas.
The ground trajectory is generally provided to the pilot, in particular by way of radiocommunication means or another customary means such as a digital data transmission link, by an air traffic controller or ground controller, but it can also, in certain cases, be chosen freely by the pilot.
The trajectory is defined in the form of a succession of elements of the airport domain, and it indicates a pathway making it possible to attain, from one point (or region) of the airport domain, another point (or region) of this domain.
Any portion of the domain, whether or not designated by a name, and identified as a distinct and delimited part of the domain, is called an element of the airport domain. An element may optionally overlap one or more others. The takeoff and landing runways, the trafficways or taxiways, the turn-around areas, the waiting zones, the stop bars, the stopping positions (stand), the maneuvering areas and the parking areas are in particular designated as elements.
Knowing the ground trajectory to be followed, the pilot acts on the aforesaid piloting facilities, so as to control the longitudinal movements of the aircraft on the ground, in such a way as to pilot the aircraft, in particular during a taxiing phase, at a speed compatible, in particular, with the airport regulations and the comfort of the passengers.
Such manual piloting of an aircraft on the ground constitutes a significant workload for the pilot. The latter must in fact follow the scheduled trajectory by controlling the speed of the aircraft with the engine thrust levers and with the brake pedals, while taking care not to depart from the pavement designed for the rolling of the aircraft, and while simultaneously monitoring the exterior environment, and in particular:                the movements of the other vehicles traveling around the airport domain, in particular aircraft currently rolling on the ground, taking off or landing, cars, trucks, etc.; and        the obstacles present around the aircraft and liable to cause a collision with the latter, in particular buildings, gangways, antennas, indication and signaling panels, and other vehicles on the ground, stationary or otherwise (aircraft, cars, trucks, mobile gangways).        
This significant workload may, consequently, influence the pilot's vigilance, and lead, in particular, to the following of an unscheduled trajectory, departures from the pavement designed for the rolling of the aircraft, and collisions with other vehicles or obstacles that may lead to significant damage to equipment and humans.
Additionally, when a speed profile associated with the trajectory to be followed is available, the manual piloting of an aircraft on the ground is not optimal in terms of use of the actuators. Specifically, the significant response time of the actuators, in particular that of the engines, can give rise to significant transient deviations in speed between the setpoint and the actual tracking, the consequence of which is to give rise to not-inconsiderable delays in the arrival time scheduled by the speed profile. These limitations play a part in particular in the congestion of large national and international airports and in the delays that penalize both airlines and passengers.
Furthermore, although regulatory and operational limits exist, the speed of the aircraft is left to the free judgment of the pilot. Specifically, no device currently exists which is capable of limiting an excessive speed of the aircraft while rolling on the ground, such as to maintain the speed within limits compatible with, for example, the airport regulations, the comfort of the passengers, the state of the pavement and tires, and the loads on the main gear of the aircraft.